The present invention relates in general to a valve by which fluid pressure is introduced into a pressure-receiving vessel, and which can automatically reduce the inner pressure within the vessel and maintain an inner pressure in the vessel at a preselected minimum value. The valve can be used in a variety of applications, including an inlet valve for pressurizing an air chamber in an air chamber shock absorber combination.
Air chamber shock absorbers have been known for many years. Such shock absorbers typically comprise a conventional piston and cylinder type shock absorber and an outer tubular member connected with the outwardly extending end of the piston rod of the shock absorber and disposed in surrounding relation with the cylinder of the shock absorber. A folded flexible air sleeve is provided between the outer tubular member and the outer tubular surface of the shock absorber so as to define therewith an air chamber capable of supporting a portion of the load of the sprung mass of the vehicle on the unsprung mass thereof. One example of such an air shock is disclosed in U.S. Pat. No. 3,149,830.
Operation of the air shock requires that at least a minimum pressure be maintained in the air chamber in order for the air sleeve to have a proper rolling action. If, for some reason, the air pressure in the air chamber is lost, the air sleeve may fold in on itself, creating a double fold which causes the shock absorber to lock up, resulting in failure of the load carrying capacity of the shock absorber. Even if the air sleeve does not develop a double fold, the lack of sufficient air pressure increases friction on the sleeve which ultimately results in the destruction of the sleeve. Air pressure may be lost, for example, if a leak develops in the conduit system that typically interconnects two such shock absorbers mounted on a vehicle.
The problem of air pressure loss has been recognized for many years and various solutions have been proposed. One such solution, proposed in U.S. Pat. No. 3,149,830, is to mount a conventional tire valve, which includes a conventional check valve, on the outer tubular member of the air shock. The tire valve permits pressurized air to be introduced into the air chamber, and the check valve is normally spring pressed to prevent the air in the air chamber from communicating with the atmosphere.
While the conventional tire valve adequately functions to allow the pressurized air to be introduced into and maintained with the air chamber, the valve suffers from several disadvantages. For example, the tire valve requires that the pressurized air filling operation be precisely gauged to prevent overfilling or underfilling of the air chamber. Moreover, the tire valve does not have any means for venting or relieving an increase in pressure in the air chamber, except by manually removing the check valve.